Detecting race condition vulnerabilities in computer software applications

ABSTRACT

Testing computer software applications is performed by identifying first and second executable portions of the computer software application, where the portions are configured to access a data resource, and where at least one of the portions is configured to write to the data resource, instrumenting the computer software application by inserting one or more instrumentation instructions into one or both of the portions, where the instrumentation instruction is configured to cause execution of the portion being instrumented to be extended by a randomly-determined amount of time, and testing the computer software application in multiple iterations, where the computer software application is executed in multiple parallel execution threads, where the portions are independently executed at least partially in parallel in different threads, and where the computer software application is differently instrumented in each of the iterations.

DOMESTIC PRIORITY

This application is a continuation of the legally related U.S.application Ser. No. 14/040,884 filed Sep. 30, 2013, which is fullyincorporated herein by reference.

BACKGROUND

The present disclosure relates to testing computer software applicationsin general, and more particularly to detecting race conditionvulnerabilities in computer software applications.

Race conditions are often the cause of subtle functional bugs inmulti-threaded software systems. Beyond functional problems, raceconditions can also potentially lead to security vulnerabilities. Forexample, in one well-known race condition example an attacker may readand alter protected files in the Unix™ file system. In anotherwell-known example, race conditions arise due to interaction between aweb-based application and an underlying relational database, therebyexposing the database to unauthorized access.

Discovering race conditions is challenging in that, by definition, theymanifest only in specific thread interleavings. Static analysis suffersfrom inherent limitations in modeling thread interleavings in a soundand accurate manner, and thus typically yields highly inaccurate resultsin detecting race conditions in industry-scale applications wherescalability is key. Dynamic testing, on the other hand, is challenged bythe fact that most thread interleavings do not highlight a latent racecondition, and thus running the subject application a small number oftimes is unlikely to yield satisfactory coverage. Checking all possibleinterleavings is also impractical for large applications, and thuseffective testing for data races remains a challenge.

SUMMARY

In one embodiment of the present invention, a method is provided fortesting computer software applications. The method includes identifyinga first executable portion of a computer software application and asecond executable portion of the computer software application, wherethe first and second executable portions are configured to access a dataresource, and where at least one of the first and second executableportions is configured to write to the data resource, instrumenting thecomputer software application by inserting at least one instrumentationinstruction into at least one of the first and second executableportions, where the instrumentation instruction is configured to causeexecution of the portion being instrumented to be extended by arandomly-determined amount of time, and testing the computer softwareapplication in each of multiple iterations, where the computer softwareapplication is executed in multiple parallel execution threads, wherethe first and second executable portions are independently executed atleast partially in parallel in different ones of the threads, and wherethe computer software application is differently instrumented in each ofthe iterations.

In other aspects of the invention systems and computer program productsembodying the invention are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with theappended drawings in which:

FIG. 1 is a simplified conceptual illustration of a system for testingcomputer software applications, constructed and operative in accordancewith an embodiment of the invention;

FIG. 2 is a simplified flowchart illustration of an exemplary method ofoperation of the system of FIG. 1, operative in accordance with anembodiment of the invention;

FIG. 3 is a simplified source code example for illustrating the systemof FIG. 1 and method of FIG. 2; and

FIG. 4 is a simplified block diagram illustration of an exemplaryhardware implementation of a computing system, constructed and operativein accordance with an embodiment of the invention.

DETAILED DESCRIPTION

The embodiments of the present invention will now be described, althoughthe description is intended to be illustrative of the present inventionas a whole, and is not to be construed as limiting to the embodimentsshown. It is appreciated that various modifications may occur to thoseskilled in the art that, while not specifically shown herein, arenevertheless within the true spirit and scope of the present invention.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical datastorage device, a magnetic data storage device, or any suitablecombination of the foregoing. In the context of this document, acomputer readable storage medium may be any tangible medium that cancontain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java™ Smalltalk™, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Reference is now made to FIG. 1 which is a simplified conceptualillustration of a system for testing computer software applications,constructed and operative in accordance with an embodiment of thepresent invention. In the system of FIG. 1, a static analyzer 100 isconfigured to identify, using conventional static analysis techniques, adata interdependency between a first executable portion 102 of acomputer software application 104 and a second executable portion 106 ofcomputer software application 104, where first and second executableportions 102 and 106 are each configured to access a data resource 108,such as by reading and/or writing to the same program variable ordatabase record, and where one or both of the first and secondexecutable portions 102 and 106 are configured to write to data resource108. Computer software application 104 may be any type of softwareapplication, including those configured for use with mainframe anddesktop computers and mobile computing devices. For example, computersoftware application 104 may be a “web” application including HypertextMarkup Language (HTML)-encoded web pages that may be hosted by acomputer server and accessed by one or more client computers via acomputer network, such as the Internet. Such web applications mayinclude client-side scripting. Thus, for example, first and secondexecutable portions 102 and 106 may be separate JavaScript™ methodswithin the same HTML-encoded web page of a web application.

An instrumentation manager 110 is configured to instrument computersoftware application 104 by inserting one or more instrumentationinstructions into one or both of first and second executable portions102 and 106, where the instrumentation instructions are configured tocause execution of the portion being instrumented to be extended by arandomly-determined amount of time, e.g., on the order of tens orhundreds of milliseconds, such as where any of the instrumentationinstructions causes an operation to be performed for the duration of arandomly-determined amount of time. In an embodiment, instrumentationmanager 110 inserts such instrumentation instruction just before and/orjust after any, and every, location where data resource 108 is read orwritten to.

A software tester 112 is configured to test computer softwareapplication 104 over multiple iterations using conventions techniques,such as black-box or glass-box testing, where computer softwareapplication 104 is instrumented differently in each of the iterations,such as where in different iterations computer software application 104includes more or fewer instrumentation instructions, is instrumented indifferent locations, and/or where the randomly-determined amount of timeassociated with each of the instrumentation instructions varies fromiteration to iteration. During each iteration, computer softwareapplication 104 is executed in two or more parallel execution threads,where first and second executable portions 102 and 106 are independentlyexecuted in parallel, or partly in parallel, in different ones of thethreads. In an embodiment, software tester 112 is also configured toidentify a race condition vulnerability associated with computersoftware application 104 if different values of data resource 108 aredetected after different ones of the iterations. Additionally, oralternatively, software tester 112 is configured to identify a racecondition vulnerability associated with computer software application104 if it determines that during one of the iterations first executableportion 102 writes to data resource 108 before second executable portion106 accesses the data resource, and during a different one of theiterations second executable portion 106 accesses data resource 108before first executable portion 102 writes to data resource 108.

Any of the elements shown in FIG. 1 may be implemented by a computer,such as computer 114, by implementing any of the elements in computerhardware and/or in computer software embodied in a non-transitory,computer-readable storage medium in accordance with conventionaltechniques.

Reference is now made to FIG. 2, which is a simplified flowchartillustration of an exemplary method of operation of the system of FIG.1, operative in accordance with an embodiment of the invention. In themethod of FIG. 2, first and second executable portions of a computersoftware application are identified as being data interdependent, whereeach portion is configured to access a data resource, and where one orboth of the portions are configured to write to the data resource (step200). The computer software application is instrumented by inserting oneor more instrumentation instructions into one or both of the first andsecond executable portions, in proximity to one or more locations wherethe data resource is accessed, where the instrumentation instructionsare configured to cause execution of the portion being instrumented tobe extended by a randomly-determined amount of time (step 202). Thecomputer software application is executed in two or more parallelexecution threads, where the first and second executable portions areindependently executed in parallel, or partly in parallel, in differentones of the threads (step 204). The computer software application istested over multiple iterations, where the computer software applicationis instrumented differently in each of the iterations (step 206). A racecondition vulnerability associated with the computer softwareapplication if different values of the data resource are detected afterdifferent ones of the iterations (step 208), and/or if it is determinedthat during one of the iterations the first executable portion writes tothe data resource before the second executable portion accesses the dataresource, and during a different one of the iterations the secondexecutable portion accesses the data resource before the firstexecutable portion writes to the data resource (step 210).

The system of FIG. 1 and method of FIG. 2 may be illustrated in thecontext of the example shown in FIG. 3, in which there are two servletslabeled servlet A and servlet B. As both servlets manipulate the samesession attribute, “uprefs”, this introduces a potential race conditionvulnerability. Furthermore, servlet B neglects to sanitize the value itreads from a database and into variable userPrefs before inserting itinto the session if it's not there already. This may introduce thefollowing vulnerable interleaving: 1) servlet A finds that “uprefs” isnot in the session; 2) servlet A then reads the value of “uprefs” fromthe database, sanitizes it, and adds it into the session object; 3)servlet B checks for “uprefs”, and also finds that it is not in thedatabase; 4) servlet A inserts “uprefs” into the session object; 5)servlet B does the same, thereby overwriting servlet A's sanitized valuewith an unsanitized value; and 6) servlet A reads “uprefs” from thesession and, assuming that it is sanitized, uses the read value in asecurity-sensitive operation. This is where a potential securityvulnerability is manifested.

The system of FIG. 1 and method of FIG. 2 may be employed to find whichexecution units in the computer software application access the samedata. Thus, for example: 1) static analysis is applied to the subjectapplication to identify accesses to shared state information bydifferent execution units; 2) instrumentation instructions includingrandom wait commands are inserted around those statements that accessthe same data (i.e., the {get/set} Attribute calls); 3) the applicationis executed in single-threaded mode; 4) dependence analysis is performedon the execution trace of the single-threaded run as provided by theinstrumentation. This reveals that servlets A and B both access theattribute “uprefs”; 5) for each pair (A,B) of execution units that werefound to access the same data in the previous step, let S_(a,1) . . .S_(a,m) and S_(b,1) . . . S_(b,n) be the statements through which theyare data-interdependent (e.g., the {get/set} Attribute calls). Theapplication is then instrumented such that a) there is a random wait(e.g., Thread.sleep call with a random value in Java™) in between everypair of consecutive statements in S_(a,1) . . . S_(a,m), as well as inS_(b,1) . . . S_(b,n); and b) the arguments to sink statements (e.g.,resp.getWriter( ).write) are checked to test whether a vulnerability hasoccurred; and 6) for each pair (A,B) of data-interdependent executionunits, an instrumented version of the subject application is run (withthe instrumentation from step 5) in a multi-threaded mode, within atesting environment (e.g., where the backend database includes test datapayloads), and test data requests are sent in parallel to theapplication instances that invoke A and B.

Thus, in the example in FIG. 3, servlets A and B would be identified asa candidate pair for testing by the end of step 4. Then, in step 6, avulnerability attributable to a race condition would typically beidentified by enforcing random waits between {set/get} Attribute callsand focusing testing on servlets A and B which allows multiple testingrounds, and thus high coverage.

Referring now to FIG. 4, block diagram 400 illustrates an exemplaryhardware implementation of a computing system in accordance with whichone or more components/methodologies of the invention (e.g.,components/methodologies described in the context of FIGS. 1-2) may beimplemented, according to an embodiment of the invention.

As shown, the techniques for controlling access to at least one resourcemay be implemented in accordance with a processor 410, a memory 412, I/Odevices 414, and a network interface 416, coupled via a computer bus 418or alternate connection arrangement.

It is to be appreciated that the term “processor” as used herein isintended to include any processing device, such as, for example, onethat includes a CPU (central processing unit) and/or other processingcircuitry. It is also to be understood that the term “processor” mayrefer to more than one processing device and that various elementsassociated with a processing device may be shared by other processingdevices.

The term “memory” as used herein is intended to include memoryassociated with a processor or CPU, such as, for example, RAM, ROM, afixed memory device (e.g., hard drive), a removable memory device (e.g.,diskette), flash memory, etc. Such memory may be considered a computerreadable storage medium.

In addition, the phrase “input/output devices” or “I/O devices” as usedherein is intended to include, for example, one or more input devices(e.g., keyboard, mouse, scanner, etc.) for entering data to theprocessing unit, and/or one or more output devices (e.g., speaker,display, printer, etc.) for presenting results associated with theprocessing unit.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

It will be appreciated that any of the elements described hereinabovemay be implemented as a computer program product embodied in acomputer-readable medium, such as in the form of computer programinstructions stored on magnetic or optical storage media or embeddedwithin computer hardware, and may be executed by or otherwise accessibleto a computer.

While the methods and apparatus herein may or may not have beendescribed with reference to specific computer hardware or software, itis appreciated that the methods and apparatus described herein may bereadily implemented in computer hardware or software using conventionaltechniques.

While the invention has been described with reference to one or morespecific embodiments, the description is intended to be illustrative ofthe invention as a whole and is not to be construed as limiting theinvention to the embodiments shown. It is appreciated that variousmodifications may occur to those skilled in the art that, while notspecifically shown herein, are nevertheless within the true spirit andscope of the invention.

What is claimed is:
 1. A system for testing computer software webapplications, the system comprising: a static analyzer configured toidentify a first executable portion of a computer software webapplication and a second executable portion of the computer software webapplication, wherein the first and second executable portions areidentified as being data interdependent and the first and secondexecutable portions are configured to access a data resource, wherein atleast one of the first and second executable portions is configured towrite to the data resource; an instrumentation manager configured toinstrument the computer software application by inserting at least oneinstrumentation instruction into at least one of the first and secondexecutable portions, and configured to insert the at least oneinstrumentation instruction proximate to a location where the dataresource is accessed, wherein the instrumentation instruction isconfigured to cause execution of the portion being instrumented to beextended by a randomly-determined amount of time; a software testerconfigured to test the computer software web application in each of aplurality of iterations, wherein the computer software web applicationis differently instrumented in each of the iterations; wherein thecomputer software web application is executed in multiple parallelexecution threads, wherein the first and second executable portions areindependently executed at least partially in parallel in different onesof the threads; wherein the software tester is configured to identify arace condition vulnerability associated with the computer software webapplication if during one of the iterations the first executable portionwrites to the data resource before the second executable portionaccesses the data resource, and during a different one of the iterationsthe second executable portion accesses the data resource before thefirst executable portion writes to the data resource; and wherein thestatic analyzer, instrumentation manager, and software tester are inimplemented in a computer hardware.